Voltage Regulation

The terminal voltage of an alternating-current generator changes with change in load in a manner similar to that of a direct-current shunt generator. Thus,

However, under some conditions of load the terminal voltage of an alternating-current generator will rise above that at no load. Fig. 20-3 shows how this phenomenon can occur. When the terminal voltage is adjusted to
normal 220 volts with a load of 100% power factor, the necessary generated voltage is 302 volts. When the power factor of the load is changed to 50% lagging without change of load current or of field excitation, the terminal voltage becomes only 176 volts. Under similar conditions, but with a load power factor of 50% leading, the terminal voltage becomes 352 volts, although the voltage produced by the d-c field winding is only 302 volts. The rest of the 352 volts are produced by the magnetizing effect of the leading component of current in the stator.

Fig. 20-3. Terminal Voltage of A-C Generator

Fig. 20-4 shows representative terminal-voltage curves as a function of load in amperes for power factors of 100%, 50% leading, and 50% lagging.